This invention relates to the application of screw controlled contacts to all types of devices and particularly to miniature electric switches, where the operator selects, out of many controlled circuits, those to be opened or closed by manually actuated switch contacts. There are known in the art, miniature slide and rocker switches performing functions outlined above, however, the pressure between their contacts in the "ON" position is very light in order to insure easy adjustment and long life. This in turn causes their contact resistance to vary from 30 to 100 milliohms, precluding their usage in applications requiring current switching capability of more than a couple of hundred milliamps and also in precision resistance circuits, where minute resistance variations could affect overall circuit accuracy such as in decades, bridges, dividers and testers using resistors, inductors and capacitors of low ohmic, high current and/or capacitive and inductive values.
There are also known in the art, screw acuated switches such as described in U.S. Pat. No. 4,027,128 granted on May 31, 1977 to Richard B. Walker, or U.S. Pat. No. 4,004,119 granted on Jan. 18, 1977 to Marc R. Latour which bypass the disadvantages outlined above, but which have their own problems; precluding wide application, such as:
a. Switch functions which are limited to printed circuits and "on-off" operations.
b. There is no way of knowing whether the switch is "on" or "off" just by looking at it.
c. The screw contact is all metal, therefore, capable of causing electric shock to an unsuspecting user. (When used in High Voltage circuits).
d. The screw contacts can be easily removed and misplaced, making the switch inoperable.
e. Switch construction is such that switch widths of 0.100" are not feasible, although required by the electronic industry.
Switches available in the art are generally limited to only a few specific combinations of poles and positions because of the molding process used in making switch housings. The molding process requires substantial capital investment in tooling and is suitable for mass production of identical parts but not for many design variants required by the industry.
Rocker and slider switches available in the art are also limited to a certain maximum number of poles and positions, because frictional resistance, which is directly proportional to the number of poles, renders some switches with large numbers of poles inoperable when ganged together. Similar considerations apply to switch life which, due to wear of sliding contacts, becomes considerably shorter in conventionally designed switches as the number of switch positions increases.